The present invention relates to an electric motor having a coaxially associated pump for a coolant circuit, in particular in a system with temperature transfer and/or heat transfer, a shaft assembly transmitting a torque from the electric motor to at least one impeller arranged in the pump housing within housing parts in the form of a hermetically sealed pressure enclosure, and a flywheel being arranged between the electric motor and the pump housing, all of the rotating parts being arranged within a hermetically sealed motor/pump unit, and the motor/pump unit being filled with fluid.
It is known to use motor/pump units which are equipped with a flywheel in power stations which are equipped with heat generators and have temperature and/or heat transfer devices. This is a safety measure in order to be able to ensure that a coolant circulation through the pump is maintained for a minimum period of time as a result of the inertial capacity of a flywheel if a fault should occur. Due to the moment of inertia of the flywheel, an electric motor of this type continues to rotoate even in the event of a power failure, and in this case the motor/pump unit conveys an amount of coolant. Although the amount of coolant is reduced, it is sufficient to ensure heat dissipation in a heat transfer device until the heat generator has been reliably switched off.
U.S. Pat. No. 3,960,034 discloses a so-called dry electric motor, in which the motor and the flywheel are cooled with air. In addition, the flywheel in this device is equipped with a protective device in order to rule out any danger to the surroundings as a result of an exploding flywheel in the event of excessive speeds.
However, in motor/pump units without a shaft seal, as disclosed in U.S. Pat. Nos. 4,084 876 or 4,084,924 (=DE 2,807,876), a hydrodynamic frictional resistance is produced by a motor filled with a coolant and by a flywheel rotating in the coolant. Rotation of the flywheel in the coolant, which often is water, results in a high power loss due to the hydrodynamic friction and the production of thermal energy. This reduces the overall efficiency of the pump, the motor and the flywheel. This motor/pump unit has a thermal barrier between the pump part and the motor part which has a thin housing neck in order to keep the thermal conduction between the hot pump housing and the cooled motor housing as low as possible. At the front end of the motor housing and within a pressure-tight common housing, a flywheel, which is driven by the shaft assembly, is located behind the thermal barrier. In addition, the flywheel is surrounded by an outer cover, which is mounted such that it can rotate in the housing and has inlet openings for the fluid located in the motor housing, in order to reduce the hydrodynamic frictional losses. During operation, the outer cover assumes an average speed which is less than the speed of the flywheel owing to the hydrodynamic friction surfaces between the housing, the outer cover and the flywheel. This should result in a reduction in the frictional losses on the flywheel arranged in the cooler motor part.
An electric motor in the form of a split-cage motor for a motor/pump unit having a flywheel is disclosed in U.S. Pat. No. 4,886,430 (=EP 351,488). The flywheel in the form of a bearing element is formed within the housing parts forming a pressure enclosure, in the region of a pressure-side pump housing cover of the encapsulated motor/pump unit filled with fluid. The flywheel takes on the radial bearing function for the shaft assembly in the region of the pump housing. In addition, since the flywheel is also in the form of an axial bearing, in contrast to the solution according to U.S. Pat. No. 4,084,924, an axial bearing arrangement at the motor end remote from the pump has been omitted.
A pot-shaped insert is arranged in the housing as an integrated thermal barrier between the pump housing and the flywheel absorbing the bearing forces. This thermal barrier is provided with insulating air chambers on the outside and opposite the pump part. Additional external fluid cooling is arranged on its inside facing the flywheel front end. A wall element absorbing bearing forces is also arranged between the fluid cooling and the front end, near to the pump, of the flywheel. Due to the design as a split-cage motor/pump unit, the flywheel chamber and the rotor chamber of the electric motor are filled with the conveyed fluid to be pumped, and these chambers are subjected to the same pressure as the pump housing, while the stator chamber of the motor is designed to be dry. A heat exchanger surrounds the motor, and the water which lubricates and cools bearing elements bearing against the flywheel, flows through the heat exchanger. This cooling circuit for the motor, the radial and axial bearings and the flywheel also flows through the flywheel itself. Such an arrangement, however, weakens the spider/shaft connection of the flywheel.